[Access] Expand MCP portal troubleshooting section

[kennyj42]

What this PR does

Expands the troubleshooting section from 2 entries to 10, covering:

• 522 errors -- CNAME misconfiguration (especially Terraform users)
• Stuck in Waiting status -- upstream server unreachable or wrong URL
• Stale status -- admin credential expired but user tokens still work
• Unauthorized errors -- token expiry for both user and admin credential paths
• Gateway routing failures -- SSE transport incompatibility, DLP blocks
• mcp-remote connection issues -- version, configuration format, credential cache
• Wrong portal homepage name -- Access team name vs portal name confusion

Why

The previous troubleshooting section had only 2 entries for a complex multi-component feature. Every issue documented here came from real incidents:

• 522 errors: MCP-108 (customer usespeak.dev)
• Gateway/DLP failures: ESCALATION-2034 (Aledade)
• Homepage name: Reported in MCP Portal Team chat (Apr 29)
• mcp-remote issues: Multiple internal reports
• Stale status: Discovered in code review (distinct from Error status)